This invention relates to a tube joint capable of connecting square tubes; and more particularly it relates to a tube joint made of metal such as zinc and the like which comprises a plurality of joint rods having protruding knurling tools with wide root ends and narrow pointed ends at the central parts of upper and lower surfaces and of right and left sides of a square prism forming each knurling tool. Each corner of the prism is cut off to form a fixed groove extending from the pointed end to the root end. A slight arcuate-shaped protuberance is provided at the central part of each said longitudinal knurling tool. The knurling tool and its protuberance force a joint rod and a plurality of joint rods are connected at their root ends to form the tube joint. Each of the rods has an outer diameter equal to, or slightly larger than the inner diameter of a square pipe into which said outer diameter of the diagonal in the protuberant part of said knurling tool corresponding to the square prism is inserted, in arbitary directions at the connecting part thereof.
The conventional tube joint is made of metals, e.g., as shown in Japanese Utility Model Publication No. 67--22992 and is difficult to connect or detach because a screw bolt is locked by a spanner (as a bolt piece). Further, a method of inserting a tapered plastic material as a packing between the tube and metallic joint has recently been used, but this method has the defect of requiring the use of a wooden hammer in inserting or removing said tapered plastic materials and does not have good efficiency in operation. Further, a tube joint for connecting square pipe which uses a longitudinal knurling tool has recently been developed. However, this tool has been unsatisfactory because it has a smooth plane of the longitudinal knurling tool making contact with the inner diameter of a pipe.
Accordingly, a tube joint made in accordance with the present invention is a novel joint based upon a fundamentally improved technique which avoids the conventional defects.